Salinity in general is a bit on the low side of things, however I doubt that's the reason for the spots. Also doubt that turning the UV light off would have caused that. Maybe what you moved around has stirred up something and that has resulted in it..

Salinity in general is a bit on the low side of things, however I doubt that's the reason for the spots. Also doubt that turning the UV light off would have caused that. Maybe what you moved around has stirred up something and that has resulted in it..

I see a small cut on the left-hand side of the atlantic blue tang.
The cut could've been a scratch against a rock or something I assume.
She is quite a wild one and loves swimming laps around the tank so anything is possible.

See the cut here:

I suspect that the cut got infected and that the tang is now sick.
There aren't any crabs or aggressive fish in the tank that would've caused this.
All equipment is enclosed as well so no way she could've ended up in a power head.

So that explains it. It's the only thing I can think of.

I still don't think she'll make it... her body is full of brown spots.

I'll post back here in a few days and let you know what happened. Please wish me luck.

I lost a sohal tang after a while with this same sickness. It is apparently a common disease/parasite in tangs. My tang cleared up after a while but I then lost him to whitespot. Anyway, sorry for ur loss buddy